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[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

** Also affects: linux-raspi2 (Ubuntu Xenial)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1703802

Title:
  Overlay files don't get applied

Status in linux-raspi2 package in Ubuntu:
  New
Status in linux-raspi2 source package in Xenial:
  New

Bug description:
  Impact:

  While working on a bug that involved loading an overlay dtb files upon
  boot, i noticed that, no matter what i put in
  config.txt::dtoverlay=..., no overlay was loaded at all.

  After further investigation i found that recently (~April 2017), the
  raspberry BSP changed the overlay files suffix from -overlay.dtb to
  .dtbo, and while the upstream bootloader was updated to accept the new
  scheme, we keep shipping an older bootloader in the the archive that
  didn't know about this change.

  To make this bug more annoying, the bootloader doesn't emit an error
  or a warning if it fails to load an overlay, it silently ignores it
  and keep going.

  Ubuntu core #stable isn't affected by this bug since it's shipping
  it's own overlay files in a static tarball (using the old scheme), and
  #edge (that is where new daily images are built) is shipping an older
  kernel with the old scheme.

  While #beta and #candidates should be affected.

  Fix:

  A way to fix this bug would be to update the raspi2 bootloader to a
  more recent version, but since updating it has proven challenging in
  the past (multiple images from multiple sources, #updates vs
  #security, different boot configs, etc), i'm taking a more
  straightforward approach by reverting the dtb overlay files rename
  back to the previous scheme.

  With that said, i'm concurrently opening another LP bug (1703799)
  because we must update the bootloader and revert this fix as soon as
  the new bootloader lands in the archive.

  How to test:

  The are different ways you can test this (like modifying the config.txt::dtoverlay=... parameter  and then checking that the corresponding hardware started to work, but then you would never know if it's a kernel driver problem, a dtb merge problem, wrong wiring, failing hardware, etc), but the best way is to use the dtc to dump out the dts structure before and after the dtoverlay
  modification and then diff the two:

  vanilla image:

  $ dtc -I fs -O dts /proc/device-tree > pi3-vanilla.dts

  now install the new kernel with the revert (dpkg -i ... or snap
  install ...), modify dtoverlay, reboot and dump again:

  # echo "dtoverlay=vc4-kms-v3d" >> /boot/firmware/config.txt
  # reboot

  $ dtc -I fs -O dts /proc/device-tree > pi3-vc4.dts

  check if the dtb passed to the kernel has changed:

  $ diff -du pi3-vanilla.dts pi3-vc4.dts
  [check that there's actually a diff and something sensible was applied]

  if you are doing this on ubuntu-core, config.txt is located in
  /boot/uboot/config.txt, while if you are doing this in ubuntu classic,
  remember to manually copy the overlay files that are shipped with the
  new kernel:

  # rm -rf /boot/firmware/overlays
  # cp /lib/firmware/`uname -r`/device-tree/overlays /boot/firmware

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